--- a/gfx/thebes/gfxDWriteFontList.cpp
+++ b/gfx/thebes/gfxDWriteFontList.cpp
@@ -1796,16 +1796,17 @@ public:
     IFACEMETHODIMP MoveNext(BOOL * hasCurrentFile);
 
     IFACEMETHODIMP GetCurrentFontFile(IDWriteFontFile ** fontFile);
 
 private:
     BundledFontFileEnumerator() = delete;
     BundledFontFileEnumerator(const BundledFontFileEnumerator&) = delete;
     BundledFontFileEnumerator& operator=(const BundledFontFileEnumerator&) = delete;
+    virtual ~BundledFontFileEnumerator() {}
 
     nsRefPtr<IDWriteFactory>      mFactory;
 
     nsCOMPtr<nsIFile>             mFontDir;
     nsCOMPtr<nsISimpleEnumerator> mEntries;
     nsCOMPtr<nsISupports>         mCurrent;
 };
 
@@ -1863,16 +1864,17 @@ public:
         IDWriteFactory *aFactory,
         const void *aCollectionKey,
         UINT32 aCollectionKeySize,
         IDWriteFontFileEnumerator **aFontFileEnumerator);
 
 private:
     BundledFontLoader(const BundledFontLoader&) = delete;
     BundledFontLoader& operator=(const BundledFontLoader&) = delete;
+    virtual ~BundledFontLoader() { }
 };
 
 IFACEMETHODIMP
 BundledFontLoader::CreateEnumeratorFromKey(
     IDWriteFactory *aFactory,
     const void *aCollectionKey,
     UINT32  aCollectionKeySize,
     IDWriteFontFileEnumerator **aFontFileEnumerator)